Thermoplastic compositions containing polyphenylene ether (or oxide) in admixture with alkenyl aromatic resins are well-known. Examples are, for example, described in U.S. Pat. No. 3,383,435 of Eric P. Cizek. Such compositions are most generally employed in the production of molded and/or extruded articles.
It is known in the art that various of the properties of these compound compositions may be further improved by copolymerizing the alkenyl aromatics with other monomers or by blending with other resins. Modifiers such as butadiene, for example, are customarily incorporated into the alkenyl aromatic resins to improve the properties of the resultant compositions. Such rubber-modified resins provide means for overcoming various physical drawbacks of alkenyl aromatic resins, particularly polystyrene, while simultaneously facilitating the processing of polyphenylene ethers.
As is described in the art, butadiene modification of alkenyl aromatic resins may take many forms. Polybutadiene or copolymers partially derived from butadiene may be graft, block or otherwise polymerized with such alkenyl aromatic resins. The resultant product may also be unsaturated or saturated (for example, by subsequent hydrogenation) without loss of desirability.
Other rubber-modifiers are also known. In, for example, U.S. Pat. No. 3,658,945 of Nakashlo et al, it is disclosed that alkenyl aromatic resins may be graft-modified onto ethylene-.alpha.-olefin-polyene terpolymer. From 0.5 to 15% of terpolymer by total composition weight, where the graft copolymer contains from 5 to 80% of styrene compound, is indicated to enhance impact strength at levels up to about 30% of copolymer by total compositions weight. Further rubber-modified graft copolymers are described in U.S. Pat. Nos. 3,943,191; 3,959,211; 3,974,235; 4,101,503; 4,101,504; 4,101,505 and 4,102,850 of Glenn D. Cooper et al and elsewhere.
Polyphenylene ether-alkenyl aromatic resins compositions (particularly those having rubber-modified alkenyl aromatic resin) generally possess outstanding physical properties. A shortcoming of these compositions, however, is their tendency to accumulate surface electrostatic charges. Theremoplastic materials having characteristic resistivities in the range of from about 10.sup.10 to 10.sup.12 ohms normally do not hold static charges. On the other hand, thermoplastic materials characterized by resistivities in the range of from about 10.sup.16 to 10.sup.18 ohms often develop high static voltages, and polyphenylene ether-alkenyl aromatic resins are often in this latter group.
Such static charges develop during processing and/or during normal use after molding. They are undesirable for a number of reasons: surface static charges readily attract dust and other contaminants which are unsightly and difficult to clean; often the contaminants or static charges themselves cause processing problems; the charges may accumulate to a level where an unpleasant electrical shock is imparted upon touching. In addition, a high level of static charges in a molded part covering sensitive electronic equipment may be undesirable.
It is therefore an object of the present invention to produce thermoplastic compositions having a low resistivity and which will thereby have improved properties, in particular for electrical applications.